SAN FRANCISCO -- All Tara Hui wanted to do was plant some pears and plums and cherries for the residents of her sunny, working-class neighborhood, a place with no grocery stores and limited access to fresh produce.

But officials in this arboreally challenged city, which rose from beneath a blanket of sand dunes, don't allow fruit trees along San Francisco's sidewalks, fearing the mess, the rodents and the lawsuits that might follow.

So when a nonprofit planted a purple-leaf plum in front of Hui's Visitacion Valley bungalow 31/2 years ago - all flowers and no fruit, so it was on San Francisco's list of sanctioned species - the soft-spoken 41-year-old got out her grafting knife.

"I tried to advocate for planting productive trees, making my neighborhood useful, so people could have free access to at least fruit," she said. "I just wasn't getting anywhere."

Today, Hui is the force behind Guerrilla Grafters, a renegade band of idealistic produce lovers who attach fruit-growing branches onto public trees in Bay Area cities (they are loath to specify exactly where for fear of reprisal).